I. Field of the Invention
The present invention relates generally to portable communication systems. More particularly, the present invention relates to novel and improved portable communications device and accessory system which provides full-duplex asynchronous communications between a portable communication device and external accessories over a synchronous digital interface.
II. Description of the Related Art
There are presently multiple types of cellular radiotelephone systems operating. These systems include the frequency modulated (FM) advanced mobile phone system (AMPS) and two digital cellular systems: time division multiple access (TDMA and GSM), and code division multiple access (CDMA). The digital cellular systems are being implemented to handle capacity problems that AMPS is experiencing. Dual-mode CDMA/FM radiotelephones exist which are selectively operative in either FM or CDMA modes. Telecommunications Industry Association (TIA)/Electronic Industries Association (EIA) Interim Standard 95, entitled "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System" sets forth the requirements and standards for a dual-mode radiotelephone which is selectively operative in either FM or CDMA modes.
A typical portable cellular radiotelephone may be interfaced with one or more external accessories. For example, the portable telephone user may desire to use his portable radiotelephone in his car while driving, and thus interface it with a hands-free speakerphone, a power booster, and/or a voice-operated dialer. The hands-free speakerphone (or hands-free "kit") allows the user to make phone calls, via an external loudspeaker and microphone, without holding the telephone. The power booster couples radio frequency (RF) signal to and from the portable radiotelephone's own antenna, amplifying the RF signal for the higher power transmission and reception that is desirable when operating off of a car battery. A voice dialer responds to verbal commands from the user, dialing from a set of pre-programmed telephone numbers according to the voice commands. These accessories are often used at the same time as part of a car adapter kit.
In the prior art, each of these external accessories requires at least one separate interface to the portable radiotelephone. For example, consider the typical prior art portable radiotelephone accessory system illustrated in FIG. 1. The portable device 100, which could be a cellular phone, a personal communication services (PCS) phone, or similar device, comprises microphone and speaker 106, multiplexer 104, encoder/decoder (CODEC) 102, digital signal processor (DSP) 108, microprocessor 110, UART 126, transceiver 112, and antenna 111.
In operation, antenna 111 receives an RF signal which is subsequently downconverted and demodulated by transceiver 112. The demodulated digital signal is passed to DSP 108 for audio-band processing, and then to CODEC 102 for conversion to an analog voice signal. For transmission, the reverse path is followed, i.e. the analog voice signal is converted to a digital signal by CODEC 102, processed by DSP 108, and passed to transceiver 112 for upconversion and modulation before transmission on antenna 111. When portable device 100 is in a portable mode (i.e. when not connected to external accessories) microprocessor 110 configures multiplexer 104 to pass the analog voice signal to and from microphone and speaker 106, which are housed in portable device 100. However, when portable device 100 is interfaced with hands-free kit 114, microprocessor 110 configures multiplexer 104 to pass the analog voice signal, over analog interface 113, to and from auxiliary microphone and speaker 116 which are housed in hands-free kit 114. In addition, when portable device 100 is interfaced with power booster 118, RF signals are received and transmitted by external antenna 120, amplified by power booster 118, and coupled to and from antenna 111 in portable device 100.
The difficulty with the prior art is encountered when one desires to pass control commands to hands-free kit 114 or power booster 118, or to control other external accessories such as voice dialer 122. Since analog interface 113 carries analog voice signals, it is not suited to carry digital control commands to external accessories. As such, separate command interfaces 115, and 117 are necessary to pass control commands to hands-free kit 114 and power booster 118, respectively. Commands to hands-free kit 114 may include instructions to automatically turn auxiliary microphone and speaker 116 on and off, or to automatically mute the car's installed stereo during a hands-free call. Commands to power booster 118 may include transmit and receive power control commands. Furthermore, the command interfaces 115 and 117 are generally synchronous serial input/output (I/O) interfaces. Since voice dialer 122, and indeed other possible accessories, may require an asynchronous interface serial communications interface with the UART 126, and command interfaces 115 and 117 are generally unsuited for asynchronous communications, asynchronous interface 124 must be a separate interface than the others. Thus, as can be seen from FIG. 1, at least one separate interface 113, 115, 117, and 124 must be used to interface portable device 100 with each desired external accessory 114, 118, and 122 adding cost and complexity.
Another difficulty with the prior art system of FIG. 1 is that when portable device 100 is interfaced with hands-free kit 114 (i.e. when operating in hands-free mode), the normal full-duplex operation of simultaneous talk and listen is suspended. This is required to prevent undesired feedback between the auxiliary speaker and microphone 116. Typically, the hands-free mode of operation is controlled by a voice-activated switch (VOX) which switches between the talk and listen paths according to the activity level of the path. If portable device 100 is operating in an FM mode, the talk and listen paths are both simultaneously enabled during hands-free operation, however the inactive path is always attenuated to prevent acoustic oscillation. If portable device 100 is operating in a digital mode, the inactive path is muted whenever active voice frames arrive from the base station. Unfortunately, the VOX switching works well only when both portable device 100 and the calling unit are in relatively quiet environments. For instance, if the caller is in a noisy public place, and the user of portable device 100 is in hands-free operation in the relative quiet of a car interior, the caller is likely to hear only broken portions of the conversation because the VOX will favor the caller's background noise over the speech of the user of portable device 100.
What is needed is a portable communication device and accessories that communicate both voice and command data over a single flexible interface, and also provides for full-duplex communication between the portable device and the accessories.